This invention relates in general to heat shields for electrostatographic imaging systems.
Generally, electrophotographic imaging processes involve the formation and development of electrostatic latent images on the imaging surface of a photoconductive member. The photoconductive member is usually imaged by uniformly electrostatically charging the imaging surface in the dark and exposing the member to a pattern of activating electromagnetic radiation such as light, to selectively dissipate the charge in the illuminated areas of the member to form an electrostatic latent image on the imaging surface. The electrostatic latent image is then developed with a developer composition containing toner particles which are attracted to the photoconductive member in image configuration. The resulting toner image is often transferred to a suitable receiving member such as paper. The photoconductive members include single or multiple layered devices comprising homogeneous or heterogeneous inorganic or organic compositions and the like. Multiple layered photoresponsive devices comprise layers deposited on flexible thermoplastic webs coated with a thin conductive layer, for example, deposited photogenerating and transport layers as described, for example, in U.S. Pat. No. 4,265,990 and deposited hole injecting, hole transport, photogenerating and top coating of an insulating organic resin, as described, for example, in U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium and various phthalocyanines and hole transport layers containing certain diamines dispersed in inactive polycarbonate resin materials. The disclosures of each of these patents, namely, U.S. Pat. Nos. 4,265,990 and 4,251,612 are incorporated herein by reference in their entirety. Other representative patents containing layered photoresponsive devices include U.S. Pat. Nos. 3,041,116; 4,115,116; 4,047,949 and 4,081,274. These patents relate to systems that require negative charging for hole transporting layers when the photogenerating layer is beneath the transport layer.
A popular type of electrostatographic imaging system utilizes a flexible multiple layered photoreceptor supported on at least two spaced apart rollers. In compact electrophotographic copiers and printers, the various components utilized to charge, expose, develop, transfer, clean and fuse are necessarily physically located close to each other. When the system utilizes a heat fuser roll to fuse transferred toner images onto a receiving sheet, radiation from the fuser roll can strike the photoreceptor. Where the heat strikes a stationary belt photoreceptor resting at idle around a small diameter support roller such as a roller having a diameter of, for example about 19 mm, the temperature of the belt can rise significantly. This high temperature can cause permanent polymer deformation of the photoreceptor and create ripples which result in physical defects in the final toner image on the receiving sheet. These ripples are characterized by a convex ridge traversing the width of the photoreceptor web with two concave troughs parallel to the convex ridge and located on each side of the convex ridge. The two concave troughs cause two deletion bands to be observed in the final print copy. The deletion bands are believed to be due to insufficient toner transfer through poor paper to photoreceptor contact in the concave trough areas of the photoreceptor. The convex ridge is seen on the final printed image as solid density image band. This solid density image band is believed to be developed due to heat induced restic recovery of the electrical properties of the photoreceptor at the convex ridge region. More specifically, when thermoplastic photoreceptor belts are parked around rollers which are exposed to heat emitted by fuser rolls, restic recovery occurs in the exposed area of the photoreceptor and the photoreceptor properties in this region are rejuvenated, particularly following extensive photoreceptor cycling. This causes electrical properties of one segment of a photoreceptor to be different from another whereby the resulting imaged receiving sheets bear nonuniform images caused by part of the images being formed on rejuvenated segment of the photoreceptor whereas other parts of the image are formed on nonrejuvenated segments of the photoreceptor.
During fusing, contact between paper receiving sheets and fuser roll surfaces also causes loss of heat from the fuser roll surface due to the absorption of the heat by the paper. Such heat loss results in the cooling of the fuser and requires replenishment of heat energy to maintain proper fusing.
Another problem encountered in electrophotographic imaging systems is the migration of contaminants migrating from fuser rolls to selenium photoreceptor drums. Various arrangements have been made to address the migration problem. Some of these arrangements involve the use of elaborate, bulky baffles interposed between the fuser and the photoreceptor.
Manifolds have also been used between a fuser and other components of electrophotographic imaging apparatus. These manifolds occupy considerable space and limit the minimum size achievable with an electrophotographic copier or printer. Moreover, baffles utilizing circulated air require expensive and space consuming fans or blowers which also consume additional electrical power.
Large bulky manifolds and shields between a fuser roll and other components of an electrophotographic imaging system require more complex and expensive machines and reduce the space available for clearance of paper jams and servicing by technicians.